In VHS recording equipment, a control track signal is recorded on a longitudinal track at the lower edge of the tape. In 50 Hz TV systems the control track signal has a period of 40 mS. The control track signal may be counted and interpreted as time information. However, such a method requires that the recorded tape be wound to the start of the recording in order to determine the time of a recorded occurrence.
A VHS Control Track Longitudinal CTL System was introduced in 1986. This system allows one bit to be transmitted every 40 mS by a variation in time of the previously unused trailing edge of the control track servo synchronising signal. Thus a time recording is provided where a complete data word is made available every 2 seconds. However, the system has a resolution of 2 seconds and the relative coding of the frame pulses is disadvantageous.
In professional equipment, an IEC 461 standard for time code has proved effective. The standard provides a Longitudinal Time Code or LTC track which has a resolution of 500 .mu.s/bit. The standard permits items of time code and other information to be multiplexed into both a longitudinal track and a helical scanned track. However, high tape transport speeds prevents the recovery of the absolute time code values.
An object of the invention is to establish a time coding system of high resolution for a digital audio and video recording system. The time coding system will facilitate reading time code at high tape transport speeds, for example during automatic search/forward and reverse.